Switch contact spring



Sept. 30, 1952 s.. G. F. BLoMQvlsT 2,512,357

SWITCH CONTACT SPRING Filed Aug. 9, 1949 Patented Sept. 30, 1952 SWITCH CONTACT SPRING Sven Gustaf Filip Blomqvist, Stora Essingen,

Sweden, assignor of one-half to Ingenjorsfirman H. F. Rost & Soner, Djursholm, Sweden,

a Swedish firm Application August 9, 1949, serial No. 109,396 In Sweden September 6, 1948 6 Claims. (Cl. 267-1) The present invention relates generally to articles of stamped and formed elastic sheet material and devices for manufacturing said articles.

The invention can be applied to articles of metal, suchas steel, hard-rolled copper, alloys of aluminum, Phosphor bronze, brass, whitel metal and the like, as well as to articles of non-metal, for example plastics, synthetic resins and the like. Sheet materials as coming from the rolling mills or casting machines generally contain numerous stresses unevenly distributed in the sheet material. In metal rolling mills the unevenly distributed stresses are causes by the fact, that all parts lof a big sheet of metal do not have the same thickness or are not equally pressed between the rolls. When such a sheet later on is cut up in small pieces for different purposes, the inherent unevenly distributed stresses will cause the pressed lor formed articles to warp, and a uniform product cannot be obtained by merely pressing or forming such a sheet material.

When cutting out variously shaped flat articles from a raw metal sheet, the unevenly distributed stresses will remain along the edges of the cut articles apart from the inherent stresses from the rolling mill.

' If articles of elastic sheet material in mass production should have exactly alike qualities, such as exact form, exact tension and so forth, a tedious and expensive manual adjustment Work has hitherto been customary and necessary.

One object of this inventino is automatically to eliminate all such irregular and unevenly distributed stresses in one operation by means of which all manufactured articles of a certain kind will have the desired exact form and exact tension in desired parts of the article.

Objects of sheet plastic and synthetic resins often present unevenly distributed stresses in the finished product or article, due to the fact that chain molecules in the state of passing from semi-solid into solid state contract more in one direction than in other directions. These stresses later on often cause warping or rcracks in the surface. The tensile strength of a linished article of such a material is therefore often not equal in all parts.

y This is often the case, when pure synthetic resins of certain hardness is used, for example, polystyrol, vinyl-ethylene, vinyl chloride and the like.

Often plasticising and softening materials are added to avoid these internal stresses, but such additions often spoil other desirable qualities of the synthetic resin, for example, its electric qualities become worse. f

These uneven stresses can be 'eliminated ac.- cording to the present invention by stamping and forming articles of synthetic' resins or plas-r tics in a semi-solid state during the process of setting, while passing from semi-liquid or semi-'- solid to a solid state.

Another object of the invention is to procure the necessary devices for the methodl of manu facturing the 'said articles.

The present invention generally refers to an elastic sheet material, in which in desired'parts tensile stresses exceeding the limit of elasticity of the material have been simultaneously impressed upon small individual surfaces of said parts. the extension of each of said individual surfaces having been limited in at least one side of the sheet material and in at least one direction to a distance of one and a half to twice the thickness ofthe said sheet material, whereby uneven distributed stresses caused by a previous process of rolling, cutting, stamping or otherwise have been dispersed in said parts of the sheet material. y n v y The said stresses for exceeding the limitwof elasticity Aare according to the invention accomplished by providing the elastic sheetma-` terial with indentations to such a depth, for example to about half the thickness of the sheet material, that the limit of elasticity of the material will be exceeded upon the formation of said indentations.

The general idea of the invention is a'method completely and uniformly to re-distribute the stresses in an elastic sheet material by exposing the individual minute parts of the sheet material to substantial tensile stresses by simultaneously impressing indentations in one or both surfaces of the sheet material.

Another object of the invention is simultaneous-A ly to form an article, while re-dis'tribution or unifying of the stresses in the elastic sheet material takes place, whereby a double technical effectk is obtained, as will later be exemplified. y

The invention can be used generally in a great number of fields, where uniformity ,of stresses throughout the material is important and particularly when at the same time the form 'of the article must be exact.

The1 invention is particularly useful in the manufacture of contact springs for electrical switching apparatus, such as manual keys and switches, contact sets in telephone subscribers' instruments, buzzers, relays, selectors, crossbar switches and the like.

It is well known that a lot of manual adjustment work must now be applied tov Contact springs before and/or after mounting in its denite position in a set of contact springs on account of non-uniformity of the springs, which must be straightened or given a certain pre-tension to fit the particular position of the spring in the set. i

It has'- been proposed to make contact springs with a certain pre-tension by providing the spring with a permanent transverse bend dividing the spring in two parts, said two parts being inclined with respect to each other for subsequent pretensioning of the said contact spring.-

The object of such a procedure was to save or at least to simplify the adjustment work of the springs in a set for obtaining the desired contact pressure of the individual springs. This method has, however, in practice proved somewhat unsatisfactory, particularly in cases when the limits for respective contact pressure were narrow. The.

reason for this difficulty consists in the fact that the contact springs, which must have good spring qualities cannot be bent in a press by means of a tool by a single lbending action for obtaining an exact angle between the two parts of a contact spring due to the fact, that all springs do not have exactly the same thickness. It has furtherbeen very' diflicult to give a perfectly plane form to those parts of the spring which were located on each side of the bend.

In cases where so-called pretensioned springs have been used, for example in crossbar switches, manufacturers have resorted to the method of hammering in order to obtain an exact angle between the two parts of the contact spring.

The present invention eliminates all these' inconveniences, whereby a contact spring can be given an exact angle for a desired degree of pretension, and those parts of the' spring, which are located on each side of the bent part can be given any desired form in the plane of the leaf spring. These parts can thus be made perfectly plane, if desired.

According to the inventionv the leaf spring is stamped and formed between a pair of dies adapted simultaneously to impress a plurality of indentations in the spring` and to give ydesired form to' same, whereby one or both dies are provided with indentations of a saw-tooth shaped cross section, the depth of said indentations and the distance between them being so limited that the limitof elasticity of the material will be exceeded upon the formation of said indentations in'- order to disperseunevenly distributed stresses inl theshee't material.

If indentations are'provi'ded on bothv sides of the spring and ifthey are running, for example, at right angles to the longitudinal axis of the spring, the ridges of the indentations at one side of the spring should be parallel with and located in front of the grooves of the indentations'on the other side of the spring. The indentations can, however, .be arranged in directions crossing each other, so that a'square or honeycomb pattern is obtained. The indentations can further have a non-rectilinear direction, for example wave form.

When indentations are made according to the present invention so as eiciently and uniformly to rearrange the stresses in the material, I have found that good results have been obtained, when the distance between two ridges of the indentations is. about 1.5 times the thickness of the material, which distance in certain circumstances vary somewhat, for example up to 1.75 or twicethe thickness of the material. The distance should, however, preferably be less.

The depth of the indentations can be about 0.5 times the thickness of the material.

Applicant has found that leaf springs treated with indentations according to the invention at right angles to the axis of the springshow about 15% greater stiffness compared with untreated leaf springs.

This extra technical effect can be utilized in obtaining a higher contact pressure in a set of contact springs, or the bending angle for pretensoning can ibe made smaller, or a leaf spring of less thickness can be used compared to contact springs used heretofore.

Other novelties and details relating to the invention will be described and explained in connection with the accompanying drawings showing an embodiment of the invention, and in which: l

Fig. 1 shows a warped and irregularly bent contact spring before stamping and forming.

Fig. 2 and Fig. 3 show the same spring in side and top View respectively after stamping and forming according to the invention. 'I'he spring is of movable kind for a set of contact springs.

Fig. 4 shows a top view of part of a contact spring of the xed kind for a set of contact springs.

Fig. 5 is a magnified side view of part of a con,- tact spring provided with indentations according to the invention, whereby formation of acontinuous bend simultaneously has been obtained.

Fig. 6 shows a side View of a set of contact springs for a relay, in which contact springs of exact pre-tensions and forms according to the invention are used.

In Figs. 1-6 spring I is shown to havea straight, fixed and plane part a and a pre-tensioned movable part b at the free end of which contacts 2 and 3 or 4 and 5 are located. If desired, the free end part of the spring, which is provided with contacts, can be made straight and perfectly fiat.

The movable contact spring is provided with a hole 8 for freely letting through the stud 23 and stud 22 and further provided with a seat 6 free from indentations for freely engaging a' lifting tooth, for example 36 of stud 23,.

The ilxed contact spring is provided with a hole S for freely letting through the studs`22 and 23 and further provided with a seat 'I' for engag' ing a tooth, for example 31 of the fixed stud 22, upon which the fixed spring normally rests. The spring is further provided with holes II, I2 and I3 for fixing the straight part of the spring to a iixed support 20 .by means of screws 24, whereby insulators 25 are spaced between the different springs. If desired, and if the pretension of a spring should be low, a hole I4 can be provided in the movable .part near to the fixed part of the spring.

In a small narrow zone around the holes I I-'-I2 .there should be no indentations, as otherwise the ridges might be pressed into the holes and interfere with the free passage of the fastening screws 24 or with washers around same, when fastening the different springs of a set.

In Fig, 5 it is shown that the teeth of the dies have gripped the flat leaf spring and have made clear impressions in same, while due to the stiffness of the spring material the ridges between the grooves have not been filling the grooves of the dies.

In Fig. 6 is shown a set of make contact springs 26--2l, a set of break contact springs 28-29 and a set of make and break contact springs 30--32,

The xed supporting member or stud 22-34 is supported by a fixed stiff spring 2l, which also serves to guide the movable member 2335, whilethe xed and movable members 22-34 and 23--35 respectively are guided at the top by a exible spring 33.

The tension of the diierent springs can be varied at will by giving diiierent pre-tensions to diiTerent kinds of springs. Thus the tension oi' the various springs can be varied for example from to 30 or more grams at the respective contacts, depending on contact pressure desired in a break or make contact.

According to the invention any exact pretension can now be given, and after assembling a set of contact springs as shown in Fig. 6, each individual spring will be in correct position in the set and have the desired exact contact pressure, without any posterior manual adjustment whatsoever.

I claim:

1. A contact spring having a minimum of intern-al stresses for electric switches comprising a strip of resilient material having indentations pressed in both surfaces spaced sufficiently closely so that the material between adjacent indentations on opposed surfaces o f said strip is stressed beyond the initial natural elastic limit of said material, said strip surfaces comprising alternate planar and depressed areas.

2. A contact spring as set forth in claim 1, wherein said indentations are approximately half the thickness of said strip in depth and spaced apart by a distance of less than twice the thickness of said strip.

3. A contact spring as set forth in claim 1, wherein the spacing of distance is of the order of 1.5 times the thickness of the material.

4. A contact spring having a minimum of internal stresses fdr electric switches comprising a strip of resilient material having indentations pressed in both surfaces, the indentations in one surface being staggered with respect to the indentations in the other surface, said indentations being spaced closely so that the strip material in the area of said indentations is stressed beyond the initial natural elastic limit of said material, said strip surfaces comprising alternate planar and depressed areas.

5. A contact spring as set forth in claim 4,

wherein said indentations are approximately half y the thickness of said strip in depth and spaced apart by a distance of less than twice the thicknes of said strip.

6. A contact spring having a minimum of internal stresses for electric switches comprising a strip of resilient material having indentations pressed in-both surfaces spaced sufliciently closely so that the material between adjacent indentations on opposed surfaces of said strip is stressed beyond the initial natural elastic limit of said material, said indentations being approximately half the thickness of said strip in depth and spaced apart by a distance of less than twice the thickness of said strip.

SVEN GUSTAF FIIJP BLOMQVIST.

REFERENCES CITED The following references are of record in the file of this patent:

UNITEDv STATES PATENTS Number Name Date 148,589 Beecher Mar. 17, 1874 252,676 Keller et al. Jan. 24, 1882 1,139,732 Slick May 18, 1915 1,697,872. Johnson Jan. 8, 1929 1,883,137 Waller Oct. 18, 1932 1,895,590 Spencer v Jan. 31, 1933 1,960,020 McGall May 22, 1934 2,202,301 Probst May 28, 1940 2,376,026 Bennett May 12, 1945 FOREIGN PATENTS Number Country Date 1,998 Great Britain of 1858 11,706 Great Britain of 1885 

